Real-world outcomes in patients with hormone receptor positive, human epidermal growth factor receptor 2 receptor-negative advanced breast cancer and visceral metastases at baseline – advanced hormone receptor positive breast cancer registry in Australia

Abstract

Background Hormone receptor-positive, HER2− breast cancer (HR+/HER2−) represents most advanced breast cancer (ABC) cases. Patients with visceral metastases are considered to have aggressive disease, historically treated with first-line chemotherapy (CT). However, trials (RIGHT Choice, PADMA, ABIGAIL) have demonstrated that cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) combined with endocrine therapy (ET) provide superior efficacy and tolerability in this setting.

Aims To compare outcomes between first-line CDK4/6i + ET and CT in Australian patients with HR+/HER2− ABC and visceral metastases.

Methods Data were obtained from the ARORA registry, a prospective observational study capturing real-world outcomes for Australian patients with HR+/HER2− ABC. Eligible patients were aged ≥18 years, with visceral metastases diagnosed after 1 January 2020, and received first-line systemic therapy. Participants were stratified by initial treatment: CT, ET + CDK4/6i or ET monotherapy. ET monotherapy was analysed as a separate cohort and excluded from comparative progression-free survival (PFS) and overall survival (OS) analyses. Primary endpoints were (1) OS: time from metastatic diagnosis to death and (2) PFS: time to progression on first-line therapy.

Results A total of 418 patients were included, with a median age of 56 years and median follow-up of 12 months. The majority of patients (73.7%) received first-line CDK4/6i + ET. Compared with CT, CDK4/6i + ET yielded significantly longer PFS (20.0 vs 11.9 months, P = 0.0006). A trend towards improved OS was observed (28.6 vs 22.9 months, P = 0.1399).

Conclusion This real-world analysis reinforces CDK4/6i + ET as the preferred first-line treatment for HR+/HER2− ABC with visceral metastases. While selection bias cannot be excluded, these findings support the shift away from routine first-line CT. Ongoing follow-up will clarify the OS impact.